Present day data processing systems are often configured in large multi-user networks. Management of such networks may typically include the need to transfer bulk data to an endpoint, or receiver, system from a source system (or, simply, “a source”). Such large data transfers may occur within a network, for example, to distribute software updates.
Data may be distributed by multicasting the distribution to the receivers. (Multicast transmissions, within the Internet Protocol (IP) framework are transmissions from one or more sources to a group of addressees. (In IP multicast, packets are sent to the multicast group, which is identified by a single IP address, rather than addressing each packet to the individual receivers.) Generally, such multicast distributions are more efficient than unicast transmission of the bulk data.
FIG. 1 illustrates a networked data processing system 100 that may be used in conjunction with the multicast transmission of data. System 100 includes a multicast source 102 that is connected to network 104 via router 106. (Network 104 may be the Internet, however, for the purposes of the present invention, the particular network or internetwork is not significant. It suffices that a suite of standardized communication protocols exist, commonly referred to as the TCI/IP (Transmission Control Protocol/Internet Protocol) suite, or simply TCP/IP, that may be used to effect the communications across network 104.) A plurality of receivers reside on respective ones of subnetworks 108 and 110. (Network receivers may be generically referred to as “hosts” when the particular role as a receiver of multicast data need not be denoted.) Subnetwork (“subnet”) 108 includes receivers 112, 114, 116 and 118, and is connected to network 104 via router 120. Subnet 110 includes receivers 122, 124 and 126, and is connected to network 104 via router 130. Receivers may join and leave a multicast group by exchanging group membership information with a multicast router, which may be assumed for illustrative purposes to be router 120 for receivers in subnet 108 and router 130 with respect to receivers in subnet 110. A receiver may join a group by sending a membership report packet to the router, which maintains a group database (not shown). (Note, however, membership of a receiver in the “all hosts” group is automatic.) TCP/IP includes the Internet Group Management Protocol (IGMP) for the reporting of group memberships by hosts. IGMP, version 2 is described in RFC (Request for Comments) 2236, promulgated by the Internet Engineering Task Force (IETF).
Within the enterprise, many different bulk data distributions may occur. These need not necessarily target all of the receivers on the network. Receivers that are not targets of a particular distribution will ignore the data. However, in a multicast distribution, the routers will forward the data to each subnet having at least one receiver that is a member of the target group, even if that receiver itself is not a target of the distribution. Consequently, the distribution data will needlessly flow to such a subnet. Therefore, there is a need in the art for methods and systems to avoid the sending of multicast bulk distribution data on subnets having no receivers that are targets of the distribution.